The determination of cell polarity and spatiaL patterns are fundamental processes necessary for growth and development in all living organisms. Budding yeast are able to recognize and orient growth to the poles of the cell during budding. The essence of this investigation is to understand how the ellipsoidal yeast cell is able to identify the poles of the cell for budding. Haploid yeast cells bud axially in which the bud site is restricted to the previous region of cell division. Diploid yeast cells bud bipolarly (at either pole). Proteins which are necessary for the recognition of the previous cell division site have been previously identified. This proposed research outlines experiments aimed to identify proteins which mark both poles of the cell for bipolar budding. By using pseudohyphal growth as a screen, bipolar-defective mutants have already been identified, and further complementation analysis is in progress. The specific aim of this proposed research is to clone, sequence and characterize these genes involved in the control of bipolar budding and, therefore, the recognition of the poles within yeast cells. The BUD1, BUD2 and BUD5 proteins presumably control bud-site selection through a GTPase signal transduction pathway similar to the H-ras GTPase cycle in humans. The proteins which this proposal intends to identify most likely control this bud-site selection GTPase cycle. Ras proteins and ras-related GTPases have been implicated to play a major role in human cancer formation (Bos, 1989). Thus, identification of factors specific to bipolar budding which likely regulate the BUD1 GTPase cycle should provide further insights into the control of ras-related GTPases.